These Large side bags will fit Large/ XLarge/XXLarge Doggie Stylz Harnesses. The Medium bag is for the Medium Doggie Stylz Harness. These bags attach to the Hook & Loop piece on the side of the harness with security strap going through attached harness loop. These bags lock using zippers and cover over it to protect from dirt and rain. These bags can be used to carry treats, travel bowls and water, first aid kit, medications and much more.